nutgall

A nutlike gall. Nutgalls on certain oak trees were formerly used as a source of tannic acid for making ink and dye.

An excrescence, chiefly of the oak. See gall, 1.

A more or less round gall resembling a nut, esp. one of those produced on the oak and used in the arts. See gall, gallnut.

An enlarged growth on a tree formed in response to damage or parasite. Sometimes called just a gall.